Wide-band distributed amplifiers



April 14, 1964 B. M. soslN WIDE-BAND DISTRIBUTED AMPLIFIERS Filed June 19, 1959 .NG N ,WN Y/ NW. Ablll- --.I .i NUM m n NM l V h. v0 mw NQ The anode filter line or chain comprises two parts. One part is of uniform :characteristic impedance and comprises series arm inductances` L2 and shunt arms constituted by the output capacities (not represented) of the` valves V1, V2 and V3. R2 is a terminating resista-nce. The other par-t `of the output or anode filter chain has a characteristic impedance tapered towards the load and comprises ser-ies arm inductances L3, L4, L and L6 and shunt arms consisting of condensers C1, C2, C3, C4 and C5 in parallel with the output capacities of valves V4, V5, V6, V7 and V8 respectively. The tape-red part of the output filter is correctly terminated by a matching network and load (which are not shown) connected to terminal 2, from which the output is taken.

Inductances L1 are chosen to constitute in conjunction with the input capacities of the valves a filter of suitable pass band and characteristic impedance. The parameters of the output filter chain are such as to provide suitable characteristic impedances and pass band, and the anodes of the valves are connected to this filter chain at such points that the phase delay between the anodes of adjacent valves is substantially the same as the phase delay between their corresponding control grids.

In order to maintain a substantially constant anode voltage swing on valves V4, V5, V6, V7 and V8 the tapered portion of the output filter is so dimensioned that its characteristic impedance decreases Iin steps, lthe actual values of the characteristic impedances from -step to step being chosen in dependence on the valve characteristics according to well known theory.

Although screen grid valves are illustrated other types may be used. For example a pair of triodes in cascode connection may be substituted for each valve shown.

It will be obvious that although simple filter sections are illustrated, more complex filter sections terminated by more complex networks may be used. iln particular more than one filter section may be used between valves. Detailed filter design is, however, a Well-known technique and needs no -further discussion here.

Although the filters illustrated in FIG. 1 are low pass filters, other forms of band pass filters may be used.

=A disadvantage often encountered With wide band arnplifiers is the generation in the amplifier of second harmonies of the signal frequencies. It is therefore preferred to embody the invention in push-pull amplifier form with the input connected to two input filter chains and the output taken `from two output filter chains c g. by means of transformers. With such amplifiers second harmonics can be effectively eliminated from the output. A pushpull embodiment of the invention is illustrated by FIG. 2.

Referring to FIG. 2 the blocks A represent amplifiers each as described with reference to and illustrated in FIG. 1. Input signals are fed through a matching network (not shown) to the primary terminals 3 of an input transformer T1 having a secondary winding with an earthed centre tap. The secondary winding terminals 1 are connected to the grids of the first valves of the amplifiers A. Output signals are taken from the anode terminals 2 of the :last valves of the amplifiers A to the ends of the primary winding of an output transformer T2. The centre point of this winding is earthed and output is taken from the secondary winding to output terminals 4, -to which are connected a matching network (not shown) and the load (also not shown). The transformers T1 and T2 are of course designed to pass signals the required band of frequencies and to matchy the impedances to which they are connected. Matching networks (not shown) may be connected to the input and output sides of the amplifiers A or the transformers T1 and T2 may be designed, in manner well known per se, themselves to provide impedance matching.

I claim:

1. A distributed amplifier comprising an input filter line including a plurality of filter sections each having a pre-determined pass band; an output filter line having .4 a pre-determined pass band which includes a band of frequencies which is also included in the pass band of the input filter line; a load cnnected to said output filter line; said output lter line including a plurality of filter sections nearer the load of characteristic impedance decreasing stepwise towards the load and a plurality of filter sections farther from the load of uniform characteristic impedance; a plurality of valves having their control electrodes connected to different filter sections along said input filter line and their anodes connected to different filter sections of uniform impedance and a second plurality of valves having their control electrodes connected to different filter sections along said input filter line and their `anodes connected to different filter sections of decreasing impedance along said output filter line, wherein the delays between said anodes are substantially the same as the delays between the corresponding control electrodes; means for applying signals to said input filter line; and means for taking output from said output filter line.

2. A distributed amplifier comprising an output line including an output terminal at one end, a lplurality of valves connected to spaced points lalong said output line to feed output energy to the output terminal thereof, said line including a plurality of filter sections, remote from said output terminal, of uniform characteristic impedance and a plurality of filter sections, nearer said output terminal, of tapered decreasing characteristic impedance, said plurality of valves including a first group of valves having their anodes connected to different ones of said first mentioned plural-ity of filter sections and a second group of valves having their anodes connected to different ones of said last mentioned plurality of filter sections, said amplifier including an input filter line havin-g. a plurality of fil-ter sections, said valves hav-ing their control electrodes connected to different filter sections of said input line to receive signals through different ones of said input line filter sections wherein the delays between said anodes are substantially the same as the delays between the corresponding control electrodes.

v3. An amplifier as claimed in claim 2 wherein the characteristic impedance of the uniform filter sections of the output filter line has a high value limited by the anode capacity of the first valve of the amplifier and the number of valves connected to the said uniform filter sections of the output filter line is sufficient to provide adequate anode swing on the last of these valves for efficient operation of said last valve.

4. An amplifier as claimed in claim 2 wherein tapering is effected by a stepwise decrease of the values of series arm inductances in the said filter sections of the line towards the load and employing shunt capacitors, the capacitance of which increases towards the load.

5. An amplifier as claimed in claim 4 wherein the last-mentioned plurality of filter sections of the said filter line is constituted by `different parts of a winding, the pitch of which is varied in discrete steps over the tapered decreasing characteristic impedance filter sections of said line.

6. A push-pull amplier larrangement comprising two substantially identical amplifiers, each amplifier having an input filter line including a plurality of filter sections each having a predetermined pass band, an output filter line including a plurality of filter sections having a predetermined pass band which includes a band of frequencies which is also included in the pass band of the input filter line, an output terminal connected -to said output line, said output filter line including a plurality of filter sections nearer the output terminal of characteristic impedance decreasing stepwise toward the output terminal and a plurality of filter sections farther from the output terminal of uniform characteristic impedance, a plurality of valves having their control electrodes connected to different filter sections along said input filter line, a portion of said plurality of valves having their 5 6 anodes connected to one of said plurality of -flter sections 2,745,004 Yeo Pay Yu May 8, 1956 having decreasing stepwise impedance and another por- 2,778,8187 Bradley Jan. 27, 1957 tion 0f the valves having their anodes connected to lter 2,930,986l Kobbe et a1 Mar. 26, 1960 seotions of uniform characteristic impedance.

5 OTHER REFERENCES References Cited m the le of this patent Electronics-July 19151, pages 106411, Malkin-1ero- UNITED STATES PATENTS Second oscmography. 2,593,948 Weigand et a1 Apr. 22, 1952 lElectronic Engineering, May 1952, pages 214-219, 2,670,408 Kelley Feb. 23, 1954 .Millirnicrosecond :Pulse Techniques. 

1. A DISTRIBUTED AMPLIFER COMPRISING AN INPUT FILTER LINE INCLUDING A PLURALITY OF FILTER SECTIONS EACH HAVING A PRE-DETERMINED PASS BAND; AN OUTPUT FILTER LINE HAVING A PRE-DETERMINED PASS BAND WHICH INCLUDES A BAND OF FREQUENCIES WHICH IS ALSO INCLUDED IN THE PASS BAND OF THE INPUT FILTER LINE; A LOAD CONNECTED TO SAID OUTPUT FILTER LINE; SAID OUTPUT FILTER LINE INCLUDING A PLURALITY OF FILTER SECTIONS NEARER THE LOAD OF CHARACTERISTIC IMPEDANCE DECREASING STEPWISE TOWARDS THE LOAD AND A PLURALITY OF FILTER SECTIONS FARTHER FROM THE LOAD OF UNIFORM CHARACTERISTIC IMPEDANCE; A PLURALITY OF VALVES HAVING THEIR CONTROL ELECTRODES CONNECTED TO DIFFERENT FILTER SECTIONS ALONG SAID INPUT FILTER LINE AND THEIR ANODES CONNECTED TO DIFFERENT FILTER SECTIONS OF UNIFORM IMPEDANCE AND A SECOND PLURALITY OF VALVES HAVING THEIR CONTROL ELECTRODES CONNECTED TO DIFFERENT FILTER SECTIONS ALONG SAID INPUT FILTER LINE AND THEIR ANODES CONNECTED TO DIFFERENT FILTER SECTIONS OF DECREASING IMPEDANCE ALONG SAID OUTPUT FILTER LINE, WHEREIN THE DELAYS BETWEEN SAID ANODES ARE SUBSTANTIALLY THE SAME AS THE DELAYS BETWEEN THE CORRESPONDING CONTROL ELECTRODES; MEANS FOR APPLYING SIGNALS TO SAID INPUT FILTER LINE; AND MEANS FOR TAKING OUTPUT FROM SAID OUTPUT FILTER LINE. 